Besides superficial and cutaneous infections in the general population, fungi can cause often fatal systemic infections in immune-impaired individuals. For instance, Cryptococcus neoformans poses a serious threat to public health and is responsible for the death of more than half a million people each year. The current antifungal drug therapies are far from satisfactory and there is a critical need for alternative or adjunct therapies, including vaccination and immunotherapy. Thus it is imperative to identify and characterize Cryptococcus factors that shape the interactions between the fungus and the host. Cryptococcus can assume two morphotypes: yeast and filament. Previous studies indicate the association between the morphotype and cryptococcal virulence. The applicant's group recently discovered that the transcription factor Znf2 serves as the molecular link between morphogenesis and virulence. Znf2 dictates cell adhesion, filamentation, and sporulation. Cryptococcus cells with Znf2 overexpression stimulate protective host immune responses and lose the ability to cause fatal diseases in mouse models. One of Znf2's prominent targets is the adhesion protein (adhesin) Cfl1. Cfl1 is up-regulated during the yeast-to-filament transition and it coats the surface of hyphae and infectious spores generated from hyphae. Importantly, overexpression of Cfl1 in the yeast cells significantly alters Cryptococcus virulence. Thus Cfl1, which naturally coats the surface of Cryptococcus infectious propagules, is likely involved in the interaction between the host and the pathogen. Surprisingly, Cfl1 not only is important for the formation of complex communities (biofilm) as an adhesion protein, but the released Cfl1 also elicits neighboring cells to form complex colonies and to undergo cellular differentiation as a signaling molecule. These preliminary data lead to the hypothesis that secreted adhesins regulate fungal community behaviors via their multi-functionalities. This hypothesis will be tested by pursuing the following specific aims. (Aim 1) Elucidate the signaling network initiated by released Cfl1. (Aim 2) Characterize a compendium of potential adhesins and examine their expression pattern in yeasts, hyphae and spores. Because the initial interaction between Cryptococcus spores and the host is critical for the outcome of the infection, characterization of adhesins on the surface of Cryptococcus spores is important for advancing our understanding of Cryptococcus biology and pathogenesis. This proposed research is the first to demonstrate adhesin-mediated signaling in a non-mobile eukaryotic microbe, and the first to investigate spore adhesins in this pathogen. Given the importance of microbial adhesins in infectious diseases, this research will provide a stepping stone for further investigation of adhesins' roles in Cryptococcus pathogenesis and for future exploitation of such molecules for clinical applications.